A heat pipe is a heat-transfer device that combines the principles of both thermal conductivity and phase transition to efficiently manage the transfer of heat between two solid interfaces. At a hot interface of the heat pipe a heat transfer fluid like a liquid that is in contact with a thermally conductive solid surface turns into a vapour by absorbing heat from that surface. The heat transfer fluid is housed within a cavity of the heat pipe that is usually an encapsulated, closed hollow space to avoid any losses of the heat transfer fluid. The vapour then travels along the heat pipe to a cold interface and condenses there back into a liquid by release of the latent heat. The liquid then returns to the hot interface through either capillary action, centrifugal force, or gravity, and the cycle repeats.